1. Field of the Invention
The present invention relates to a method and apparatus for monitoring and controlling the process train of ozonation and biologically aerated filtration used in water and wastewater treatment.
2. Description of Related Art
The process of ozonation is widely used in water and wastewater treatment aiming to increase the biodegradability of organic constituents, and kill or inactivate bacterial or pathogenic species for disinfection. Biologically aerated filters (BAF) are a fixed bed fixed biofilm process for the simultaneous removal of biochemical oxygen demand (BOD), ammonia, and total suspended solids (TSS). Filter media can be sand, expanded clay, pumice, plastic beads, or other proprietary media. In BAF, process air is introduced in the system from the bottom to supply oxygen for BOD removal and nitrification. When headloss is built up due to the interception of TSS and biological growth, a cleaning routine is initiated by including air scouring, concurrent air and water washing, and water only washing. Usually, air for scouring is supplied with a separate delivery system. If excessive process air is delivered into the system, the effluent dissolved oxygen will be elevated. Under this situation, oxygen will not be a limiting factor for biological reaction, and the excessive air delivered will simply go back to the atmosphere with extra energy consumption. Similarly, if process air is not delivered sufficiently, dissolved oxygen in the effluent will drop and process becomes oxygen limiting. In this process combination, the use of ozone is intended for increasing biodegradability of the influent water (expressed as the ratio of BOD/COD) so that BOD can be utilized by the microbes attached on the filter media. Ozone underfeeding may not generate enough of an amount of BOD and compromise the performance; overfeeding, on the other hand, may not be necessary.
In the past, the processes of ozonation and biologically aerated filtration were controlled separately with little consideration of utilizing a unified parameter or indicator for process control and automation, where ozone dosage was usually predetermined and modified on site according to other process information such as influent BOD, TSS, and color, etc., without referencing a unified process indicator. Meanwhile, the aeration rate was generally pre-set with little variation during the operation of BAF.